Interference effects in the X(4260) signal

We show that the long known puzzling branching ratios of open-charm decays in e⁺e^- annihilation can be reasonably described with a simple form factor, which strongly suppresses open channels far above threshold. Application to the e⁺e^-→J/ψππ data on the X(4260) enhancement recently reported by the BABAR Collaboration [B. Aubert (BABAR Collaboration), arXiv:0808.1543] allows a good fit with a simple nonresonant cusp structure around the D_s^*D_s^* threshold. Moreover, we argue that a closer look at the data reveals an oscillatory pattern, which we model as an interference effect between a fast—OZI-allowed—and a slow—OZI-forbidden—J/ψf₀(980) mode. Other candidates for similar nonresonant enhancements are discussed.